This proposal is an approach to the problem of cell division regulation in Escherichia coli by the use of temperature-sensitive cell division mutants. These mutants grow normally at low temperature but at high temperature they do not complete septum formation - the last step of the cell cycle. At 42 degrees C, they grow as long, non-septate, multi-nucleate filaments. The genes defined by these mutations are located at numerous sites around the chromosome. Two of these genes, sep and ftsA, are the subject of this proposal. Transducing phages which carry sep and ftsA have been prepared in vivo and by recombinant DNA technology in vitro. These phages will be used to identify the products of the sep and ftsA genes, to identify the transcripts of these genes, and to determine how these genes are expressed during the cell cycle.